Many 1.65 memory sticks will run at 1.5 volts. The ram timings may be different when mixing brands and different voltage specs, but it won't hurt anything. If anything, set the speed and voltage in manual mode; use the slower speed of the two and the higher voltage. Running 1.5 volt ram at 1.6 volts won't hurt it.
Most cases you'll find that the default/standard setting of 1600MHz ram is usually 1333 or 1066 @ 1.5v. When you oc or set your memory to profile 1or XMP whatever you motherboard manufacturer calls it it will take the memory to 1600MHz and the voltage up to 1.65. If you mix memory manufacturer's brands it might or might not work. If you can match it with a second stick of the same memory you will probably me much better off.